Cancer describes a range of diseases, which result from dysregulated growth of cells of the body. Malignant cancers may develop from this dysregulated growth and subsequently spread around the body via the bloodstream or the lymphatic system, a process known as metastasis. Malignant tumours of epithelial tissues are the most common form of cancer and are responsible for the majority of cancer-related deaths in western industrialised countries. According to the Australian Institute of Health and Welfare (AIHW), on average one in three men and one in four women will develop cancer before the age of 75 years (1). In men the most common cancers are prostate, bowel and lung and in women, breast, bowel and melanoma. Identification of genes expressed specifically in tumour tissues and not in normal tissues, and analysis of their functions are useful for identifying new targets for cancer therapy.
Several genes have been implicated in various cancers. For instance, oncogenes are known to code for receptors for cellular growth factor such as epidermal growth factor. The ras gene is an oncogene that is believed to be responsible for up to 90% of all human pancreatic cancer, 50% of human colon cancers, 40% of lung cancers, and 30% of leukemias. Mutated oncogenes can become cancer-causing genes. Such mutated oncogenes code for proteins such as protein kinases and protein phosphorylating enzymes that trigger uncontrolled cell growth. EphB4 is a recently identified member of the largest known family of receptor protein tyrosine kinases. Eph receptor family members have been identified to be involved in many cellular processes including neural development, angiogenesis and vascular network assembly (2-5). As a result of interactions with their ligands, the ephrins, they mediate contact-dependent cell interactions, which regulate cell functions such as contact inhibition, cytoskeletal organisation and cell migration (6, 7).
Although a number of anti-cancer agents including growth inhibitory molecules such as cytoxic compounds have been developed in an attempt to treat cancer, there still remains a need for providing effective methods for regulating cancer.